The benzoate/nitrate/2,2′:6′,2″-terpyridine ‘blend’ in lanthanide(III) chemistry: Relevance to the separation of lanthanides and actinides by solvent extraction

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII-mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2-4 display similar structural characteristics with 1 and 5. The structures of 1-5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N'-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0-300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is -0.09(1) cm-1 based on the spin Hamiltonian Ĥ = -J(ŜGd1·ŜGd2).

Asymmetric Dinuclear Lanthanide(III) Complexes from the Use of a Ligand Derived from 2-Acetylpyridine and Picolinoylhydrazide: Synthetic, Structural and Magnetic Studies

A family of four Ln(III) complexes has been synthesized with the general formula [Ln₂(NO₃)₄(L)₂(S)] (Ln = Gd, Tb, Er, and S = H₂O; 1, 2 and 4, respectively/Ln = Dy, S = MeOH, complex 3), where HL is the flexible ditopic ligand N’-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H₂O solvates of these complexes were determined by single-crystal X-ray diffraction. The two Ln^III ions are doubly bridged by the deprotonated oxygen atoms of two “head-to-head” 2.21011 (Harris notation) L¯ ligands, forming a central, nearly rhombic {Ln^III₂(μ-OR)₂}⁴⁺ core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H₂O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L¯. The IR spectra of 1–4 are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85–300 K range reveal the presence of weak, intramolecular Gd^III∙∙∙Gd^III antiferromagnetic exchange interactions in 1 [J/k_B = −0.020(6) K based on the spin Hamiltonian Ĥ = −2J(Ŝ_Gd1∙ Ŝ_Gd2)] and probably weak antiferromagnetic Ln^III∙∙∙Ln^III exchange interactions in 2–4. Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for 3 in terms of the magnetic anisotropy axis for each Dy^III center and the oblate electron density of this metal ion. Complexes 3 and 4 are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time τ was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.

Synthesis, structure, and photoluminescent behaviour of molecular lanthanide–2-thiophenecarboxylate–2,2′:6′,2′′-terpyridine materials

A lanthanide series incorporating 2-thiophenecarboxylate and terpyridine is presented. Four structure types are observed with differences in the coordination number and nuclearity of the complexes attributed to the effects of the lanthanide contraction.

Anion-directed assembly of helical copper(ii) complexes based on a bispyridylpyrrole ligand: synthesis, structural and magnetic properties

Helical copper(ii) complexes based on a bispyridylpyrrole ligand, namely the helical polymer {[Cu₂(PDP_H)₂(N₃)₂]}n, a discrete double-helical complex [Cu₂(PDP_H)₂(NO₃)₂] and triple-helical complex [Cu₂(PDP_H)₃](OTf), were synthesized by displacement of Cl⁻ in [Cu(PDP_H)Cl].

Crystal structure of di-μ-benzato-κ(4) O:O'-bis-[aqua-(benzato-κO)(benzato-κ(2) O,O')(2,2':6',2''-terpyridine-κ(3) N,N',N'')europium(III)]-benzoic acid (1/2)

The title compound, [Eu₂(C₇H₅O₂)₆(C₁₅H₁₁N₃)₂(H₂O)₂]·2C₇H₆O₂, is a co-crystalline compound containing a dinuclear Eu^III coordination complex with inversion symmetry co-crystallized with benzoic acid in a 1:2 ratio. The Eu³⁺ ions within the dimer are nine-coordinate, containing one tridentate terpyridine, one water, and four benzoate ions, two of which bridge the Eu³⁺ ions. Of the four benzoate ligands coordinating to each Eu³⁺ position, three distinct coordination modes [monodentate, bidentate–chelating, and bidentate–bridging (twice)] are observed. Within the crystal, there are two additional uncoordinating benzoic acid mol­ecules per dinuclear complex. Within the dimer, the water bound to each Eu³⁺ ion participates in intra­molecular hydrogen bonding with a coordinating benzoate. Additionally, the carb­oxy­lic acid group on the benzoic acid participates in inter­molecular hydrogen bonding with a benzoate ligand bound to the dimer complex.